Electron tube



Feb. 7, 1928. I 1,658,478

W. DAU MANN ELECTRON TUBE Filed June 1924 Patented Feb. 1192c.

UNITED STATES PATENT oF icE.

WILHELM nAUMANN,-oE HAMB RG, GERMANY, AssreNoE T 0. n. F. Mt'rLLEn,

EoNreENEonnENEABarx, 0E HAMBURG, GERMANY, A CORPORATION 0E GER- MANY. I

Application filed June 9, 1924, Serial Nb.

My present invention relates to electron tubes of. the type employing afilamentary electrode'in conjunctionwith a co-operating electrode havinga relatively large surface. The object of this invention is to improvethe construction of tubes of this. type, particularly such as "areintended for operation at high voltages, at which there is considerabledanger of injury and even rupture of the '1 filament. g

According to my invention, the filamentary electrode is given the formof a loop or how situated partly or entirely within the co-operatingelectrode which has a concave surface directed toward the filamentaryelectrode, and apeculiar relation, explained in detail hereinafter, isestablished between the saidv two electrodes, to protect the filamentagainst injury, and to prevent accidental contact of the two electrodes.

The invention will now be explained in detail with reference to. theaccompanying drawings, in which Figs. 1 and 2 are two sections, takenaxially of the tube, but at right angles to each other, showing atypical form of my invention, together with dotted lines indicatingcertain important relations which constitute the basis of my improvedarrangement; Figs. 3 and 4 are axial sections, taken at right angles toeach other, illustratinga second form of myin'vention; Fig.5 is an axialsection of a third embodiment, which is also illustrated in partial planview in Fig. 6 and in a detail perspective view in Fig. 7 Figs. 8 and 9are respectively an elevation and a plan, with parts in sec- .tion, ofanother form of my invention, in which the large surfaced electrode iscylindr'ical; and. Figs. 10 and '11 are respectively an axial and atransverse section of a form of construction of the same general type asthat shown in Figs. 8 and 9.

, Referring particularly to Figs. 1 and 2, I will describe this exampleof my invention as follows:

()ne of the electrodes, which constitutes the anode in the use of thedevice, is formed as a dished body 1 of spherical curvature,

ment to be perfectly flexible, that the farthes t points the filamentcould reach, within ELEo'rnoN TUBE.

718,755, and in Germany June 11, 1923.

while the other electrode, which in use will be the cathode, consists ofan arched or looped filament 2, of any suitable conducting material, theends of said filament being secured to conducting supports3, asindicated at 4. The large-surfaced electrode or anode 1 is made ofsheet-metal or other suitable material. It will be understood that thetwo electrodes with the supports 3- are generally locatedwithin anevacuated bulb of any usual or approved construction; this remark willapply to all the forms of my invention illustrated in the drawings; forthe sake of clearness, the bulb and the manner of connecting theelectrodes with it have been only indicated in a general'way in Fig. 1,and any person skilled in this art will be able to provide a suitableway of arranging the saidparts within such a bulb. It will be noted thatthe major portion of the filament how 2 lies within the dished anode 1,the concave surface of which is directed toward said filament. It willalso be understood that, generally, the filament is adapted forconnection with a battery or other source of electricity locatedexteriorly of the electron tube, so that by the passage of a currentfrom such external source, the filament may be heated to the temperaturebest adapted for the particular effect to be produced in eachindividual. case. Now, in the operation of the electron tube, when thefilament is subjected to forces tending to deform it, there are twomain. requirements: First, Whatever deformation or distortion thefilament may undergo, it must never come in contact with the opposingelectrode. Second, the main resultant of the forces actingon thefilament should be such as to tend 'to give it an axial positionsubstantially as shown, in other words, the tendency of such forcesshould be to pull the filament toward theaxis (the central vertical line-in Figs. 1 and 2) rather than to deflect it laterally from said axis.Now referring to Fig. 1 it will be obvious, assuming the filathe planeof Fig. 1, will lie on an ellipse such as the filament will describe ifthe fixed points 4 are used as the foci of the ellipse. This ellipse isindicated by the dotted line E, and it will be obvious that the majorradius a of this ellipse will be equal to onehalf of the length Z of thefilament, while its minor radius 1) will be equal to where the distancebetween the two fixed filament ends 4 is designated as 2 If such anellipse is then" rotated about the axis connecting the two points 4, 4,the ellipsoid thus described will be the locus containingall thefarthest points which the filament secured at 1, 4. can reach, assuming(as stated above) such filament to be perfectly flexible, substantiallylike a string. Now, the condition that the filament shall not be able totouch the electrode 1 is evidently fulfilled by arranging said electrodeentirely outside of the ellipsoid above defined. In the projection Fig.2 the'outline of said ellipsoid would appear as a circular line E. Ifthe anode 1 were of an ellipsoidal shape parallel to the ellipsoidmentioned above, it would exert a uniform. action or attraction at allpoints on the filament, and there would be no tendency to give thelatter a definite position. In order that there may be a tendency togive the filamentary electrode an axial position, the concave surface ofthe anode 1 is made to approach the surface of the said ellipsoid moreclosely at the axial portion than at other points or portions, or inother words, the radius of curvature of said anode surface will begreater than that of the said ellipsoid; this will be clear,particularly from Fig. 1. In practice, with an anode of the generaldished form shown in Figs. 1 to 5,

- I have found that satisfactory results are obtained if the dimension[1, which I may term the height of the filament are or bow (saiddimension being but slightly smaller than the minor radius 7) ottheaforesaid ellipsoid) is made smaller than the distance of any point ofthe straight line or base 4- 1 from the nearestpoint of the concavesurface of the anode I. The curve G in Fig. 1 represents the limit casein which the distance from any point of the said base line H to thenearest point of the curve G is constant, being equal to the dimensionh.

The anode and the filamentary cathode are in axial alignment, their axiscoinciding with the longitudinal axis of the vacuum tube or electrontube.

The construction illustrated by Figs. 3

and t differs from the one shown in Figs.

1 and 2 simply by having the anode 5 bellshaped, with a curled flange,the filamentary cathode 6 having its loop or bow within the anode, andthe relations as to filament length and position of the anode relativelythereto, being governed by the same rules as explained above inconnection with Figs. 1 and 2. Y

lVhen the electron tube is intended for heavy duty, and particularlyfor. currents of great strength, incandescent filaments of considerablelength are required. Instead of employing a single filament of greatlength, it is advisable in such cases, for practical (reasons, to employa plurality of cathode loops or bows, the size of the anode surfacebeing increased correspondingly. In certain prior constructions, a fiator plane anodehas been used; this, however, would present materialdifiiculties in the case of a plurality of cathode loops facing such aplane anode, since the loops facing the marginal portion of the anodewould lie in the region of strongly unsymmetrical fields and would thusbe deflected or bent quite considerably. Furthermore, the cathode raysissuing from these marginal loops would not strike the anode portionslying next to them, but would deviate and reach points not constructedto receive the impact of such rays. Stray rays of this character areliable to injure the tube by perforating the glass bulb, especiallyduring the evacuating pperation. Again, in the special case of using theelectron tube for the generation of X-rays, rays straying from theintended path will evidently reduce the efiiciency or power of the tube,by diminishing the numof rays that become effective or avail a e.

From the above consideration, the advantage of giving the anode a shapesuch that it will enclose or surround the cathode loop or loops at leastpartly, will be apparent. The special construction adopted by me alsoneutralizes any forces tending to twist the individual loops; thisresult is another advantage of the particular proportioning of certaindimensions as explained above in connection with Figs. 1 and 2.

Several forms of my invention in which a plurality of filament loops areemployed in conjunction with a curved anode surrounding them partly orentirely, are shown in Figs. 5 to 11.

In the construction illustrated by Figs. 5, 6, and 7, the anode 7 (Fig.5), shown of spherical curvature, encloses or surrounds the loopportions of the three wires or filaments 8, 9, and 10, which areconnected in series as will be understood best from Fig. 7. One end ofthe filament 8 is secured at 11 to the conducting support 13, while tothe other secured to successive portions of said rod, forv conductingsupport 14 is secured, at 12, one end of the filament 10; the other endsof thesefilame'nts 8, 10, are secured to the ends of c the third ormiddle filament 9. The three filaments are disposed in planes which aresubstantially radial with respect to the spherically-curved anode 7. Therelation of each of the three filaments to said anode is determinedaccording to the same rules or proportions as those explained above inconnection with the construction shown in Figs. 1 and 2. a

When a very great filament lengthis required, a construction such asshown in'Figs. 8 and 9 maybe used with advantagen In this case the anodehas the shape of a cylinder 15 extending continuously around the spacewithin which the filamentsare located.

For instance, a rod 16 consisting of arefractory insulating material,(quartz being suitable), is arranged axially within said cylinder 15 andconstitutes a carrier for a series of spirally-disposed filament loopsl7 there be any unsymmetrical action of theforces tending to bend theloops lengthwise of the cylinder, these can never lead to any dangerousdistortion of the plane of the loop, for the reason that for each of.theloops theconditions explained above are observed,

. the .heightlof each loop being smaller than the distance of any pointof its base from theinner surface of the cylindrical anode 15;

' also, the special relation of the anode surface to the ellipsoiddescribed by each of the filament loop's if it were swung about its attached ends, would hold in this case in-the same manner as I haveexplained above in connection with Figs. 1- and 2. These remarks willalso apply to the further form of my invention illustrated by F igs.- 10and 11. Here the individual filament loops 21 are arranged in two sets,in an axial plane, the cylinder anode 22 being, of the same type as theanode 15 of- Figs..8 and 9, and a rod or carrier 23, extendin axially.within the anode, the bases of the laments being parallel to the anode'axls. The sev-' eral loops 21 are secured to collars 24 surrounding thecentral carrier ,rod 23, and form two sets or series arranged onopposlte v sides of the carrier, At the upper or inner,

end of the carrier, the farther ends of the last filaments or loops ofthe two sets are connected with each other asshown in Fig. 10; the otherend of one set is connected with the lead 25, and that of the other setwith a lead 26, while the several loops of the same set are connected inseries. 7

Electron tubes of the type set forth herein may be used for theproduction of-X-rays,

or for anyother purpose for which tubes of this character are adapted.It will be understood that when cylindrical anodes are em-- ployed, asin Figs. 8 to 11, such anodes would be open at least at one end, theupper end being shown openin Figs. 8 and 10.

Various modifications may be made without departing from the nature ofmy invention as set forth in the appended claims.

I claim:

1. An electron tube including an anode having a concave surface and afilamentary cathode having 'a loop located within the anode, the ends ofsaid filament being fixed, and the concave anode surface lying entirelyoutside of a rotation ellipsoid whose axis of rotation coincides with aline connecting the points at which the ends of the filament are fixed,and the axial section of said rotation ellipsoid exhibiting an ellipseWhose major radius is equal toone-half of the length of the filament,and whose minor radius'is equal to where Z designates the length of thefilament, and 2 the distance between said fixed points. 2. An electrontube including an open anode having a concave surface and a filamentarycathode having a loop located within the' anode, the ends of saidfilament being fixed, and the height of the filamentpoint of thestraight line connecting said fixed ends, from the nearest pointof theconcavesurface of said anode.

3. An electron tube including an anode loop being smaller than thedistance of any having a cylindrical concave surface, a carrier disposedaxially with respect to said anode, and a plurality of filamentarylooped cathode elementssupported by said carrier and located atdifiierent points of its length,

each of said looped elements being of a height smaller than the distanceof any point of the straight'line connecting the ends of such element,from the nearest point of .the concave surface of said anode.

4. An electron tube including an anode, having a cylindrical concavesurface, a carrier disposed axially with respect to said anode, and aplurality of filamentary cathode elements each having fixed endssupported by said carrier, the several. elements being located atdifi'erent points of the carriers length, and the concave anode surfacelying entirely outside of the ellipsoidal surfaces which the filamentaryelements would 5 describe it swung about their fixed ends.

5. An electron tube including an open anode having a concave surface anda filamentary cathode having a loop located Withspecification.

WILHELM DAUMANN.

